Method and device for compressing a composite radius

ABSTRACT

A bow wave in a composite laminate generated during part consolidation is reduced by transmitting atmospheric pressure loads to a region of the part having low compaction pressure due to bridging of a vacuum bag at an edge of the part.

TECHNICAL FIELD

This disclosure generally relates to methods and equipment for fabricating fiber reinforced resin laminates, and deals more particularly with a method and device for compressing a radius in the laminate.

BACKGROUND

Fiber reinforced resin laminates may be consolidated prior to and/or during curing in order to eliminate voids and other inconsistencies in the cured part. Consolidation may be achieved by applying pressure to the uncured laminate using vacuum bagging and/or autoclaving processes. In some cases, a caul plate is placed between the vacuum bag and certain areas of the laminate such as a radius, in order to assure that the applied pressure is evenly distributed over these areas. In some part geometries, regions of low pressure may exist over the part for any of a variety of reasons, such as bridging of the vacuum bag over certain features of the part. These low pressure areas may result in a “bow wave” being generated in the outer plies of the laminate, in which an out-of-plane wave of the plies is forced from regions of high pressure to the regions of the low pressure mentioned above. Bow waves are undesirable because they result in out-of-plane fiber distortions that may cause voids in the laminate.

Accordingly, there is a need for a method and a device for reducing bow waves in fiber reinforced resin laminates during consolidation, particularly those that may occur near the edge of a radius in the laminate. There is also a need for reducing regions areas of low pressure on the laminate caused by bridging of a vacuum bag.

SUMMARY

The disclosed method and device reduce bow waves in the laminate plies caused by bridging of a vacuum bag used to consolidate the laminate. The device is relatively simple in construction, is reusable and easily installed. The device is used to compress a region of low pressure area on the laminate, such as an edge of a radius, caused by bridging of the bag over the radius edge. The device includes a first caul covering the radius, and a second caul covering the first portion and the radius edge. The second caul may also overlie a second laminate such that consolidation pressure applied to the second laminate is transferred through the second caul onto the radius edge. In one embodiment, the first and second cauls may be integrated to form a single unit. In other embodiments, multiple devices may be joined together side-by-side. The disclosed embodiments may reduce bow waves in laminates during the consolidation process, resulting in cured parts which may exhibit reduced voids and inconsistencies, and desired mechanical properties.

According to one disclosed embodiment, a method is provided of reducing a bow wave in a composite laminate part during consolidation. The method comprises transmitting atmospheric pressure loads to a region of the part having a low compaction pressure due to bridging of a vacuum bag at an edge of the part. The region of low pressure may be located at an edge of a radius in the part. Transmitting atmospheric pressure loads may include applying the transmitted loads at the radius edge using a caul on the part at the region of low pressure.

According to another embodiment, a method is provided of reducing a bow wave produced in a region of low compaction pressure of a first uncured composite part during consolidation in a vacuum bag with a second composite part. The method comprises placing a caul device over the first and second parts covering the low pressure region, and using the caul to apply atmospheric pressure loads to the low pressure region of the first part. The region of low pressure may be along an edge of a radius on the first part. Placing the caul includes placing a first caul over the radius and the radius edge on the first part, and placing a second caul on the second part overlapping the first caul. Using the caul to apply pressure includes using the second caul to apply pressure to the first caul in the region of low pressure.

According to a further embodiment, a method is provided of compressing a radius section of a fiber reinforced laminate part during consolidation. The method comprises forming a large radius in the part adjacent the radius section, and applying compaction pressure to the part, including applying tension on the fibers in the radius section by compressing the fibers in the large radius. Forming the large radius in the part includes forming an excess curved flange on the part.

According to still another embodiment, a device is provided for reducing a bow wave at an edge of a composite laminate part during consolidation. The device comprises a caul configured to substantially conform to the shape of and apply compaction pressure to the edge. The edge may be located along a radius in the part, and the caul includes a first portion adapted to be placed on and apply pressure to the radius, and a second portion having an extremity overlying the first portion and the edge of the part. The first and second portions of the caul may be formed integral with each other.

In still another embodiment, apparatus is provided for tensioning fibers in a radius of a fiber reinforced composite laminate part during consolidation. The apparatus comprises a mandrel having a large radius in an excess flange area of the mandrel, wherein the large radius has a radius of curvature greater than that of the radius of the part.

In another embodiment, a device is provided for reducing a bow wave generated in a radius of a composite laminate part during consolidation. The device comprises a caul for applying pressure to the radius of the part. The caul includes a first portion adapted to cover the radius and an edge contiguous to the radius in which a bow wave in the part is generated. The caul further includes a second portion overlying the first portion and the edge of the part for applying pressure to the edge of the part through the second portion of the caul.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

FIG. 1 is an illustration of a side view of a composite structure assembly.

FIG. 2 is an illustration of a side view taken in the direction ‘2’ in FIG. 1.

FIG. 3 is an illustration of an enlarged sectional view showing the formation of a bow wave in the upper plies of the spar at the end of the stiffener.

FIG. 4 is an illustration of a sectional view of the composite structure assembly, showing the use of a caul device to reduce the bow wave shown in FIG. 3.

FIG. 5 is an illustration of a sectional view of a first caul forming part of the caul device shown in FIG. 4.

FIG. 6 is an illustration of an end view of a second caul forming part of the device shown in FIG. 4.

FIG. 7 is an illustration of a perspective view of the second caul.

FIG. 8 is an illustration of a perspective view of one side of the stiffener shown in FIGS. 1-4 having the second caul installed thereon.

FIG. 9 is an illustration of an isometric view of another form of the caul device being installed on the stiffener.

FIG. 10 is an illustration of a perspective view of one side of another embodiment of the caul device.

FIG. 11 is an illustration of an isometric view of the opposite side of the caul device shown in FIG. 10.

FIG. 12 is an illustration of the caul device shown in FIGS. 10 and 11 installed on a pair of the stiffeners.

FIG. 13 is an illustration of a sectional view of a laminate assembly showing an alternate method of reducing bow waves.

FIG. 14 is a simplified flow diagram illustrating a method for reducing a bow wave.

FIG. 15 is an illustration of an alternate method of reducing a bow wave.

FIG. 16 is an illustration of a flow diagram of aircraft production and service methodology.

FIG. 17 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

Referring first to FIGS. 1 and 2, a composite structure assembly 20 comprises a stiffener 21, sometimes also referred to as a first part, and a spar 22 sometimes also referred to herein as a second part. The stiffener 21 is bonded to a spar 22 by a layer of adhesive 40. The stiffener 21 may comprise a fiber reinforced resin composite, and in the illustrated example, has an I-shaped cross section formed by upper and lower flanges 24, 26 joined together by a web 28. While an I-shape cross section is shown in the Figures, the stiffener 21 may have other cross sectional shapes, such without limitation, C, J, Z, L and inverted U shapes. The spar 22 comprises a fiber reinforced resin laminate having a web 30 and a flange 32 forming an L-shaped cross section, however other cross section geometries are possible, such as, without limitation, a “C” section. The spar 22 may form, for example and without limitation, part of the airframe of an aerospace vehicle (not shown) such as a wing or a stabilizer (not shown).

The web 30 transitions to the flange 32 through a radius 34 defined between tangent points indicated by the broken lines 36 in FIG. 1. As best seen in FIG. 2, the lower flange 26 of the stiffener 21 overlies and is bonded to the upper surface 35 of the web 32. FIG. 1 illustrates a mandrel 38 for supporting the spar 22 during consolidation and curing of the spar 22. In the illustrated example, the stiffener 21 is a pre-cured part that is bonded to the spar 22, however, in other embodiments, the stiffener 21 may comprise an uncured composite part that is co-cured with the spar 22. The shapes of the stiffener 21 and the spar 22 merely illustrate a wide variety of possible part shapes and geometries.

Referring now to FIG. 3, after the stiffener 21 and the spar 22 are assembled with a layer of adhesive 40 therebetween, a vacuum bag (not shown in FIG. 3) is sealed over the assembly 20, which may then be placed in an autoclave (not shown) for consolidation and curing. The radius 34 has an upper edge 45 that is spaced from the outer end 46 of the lower flange of the stiffener 21. When evacuated, the bag may bridge over the edge 45 of the radius 34. Bridging of the bag over the edge 45 may result in a region 49 of low compaction pressure at the edge 45 when autoclave pressure P is applied during consolidation and curing of the spar 22. The applied compaction pressure P results in deformation of the fibers in the upper plies 42 along the radius 34 which urges them to move in the direction of the arrow 51 toward the region of low pressure 49. The movement of the fiber toward to the low pressure region 49 may result in the generation of a bow wave 44 in the upper plies 42 of the spar 22 as the plies 42 are being compressed in the other areas of the radius 34. This bow wave 44 may result wrinkles, voids or other undesired inconsistencies in the spar 22 following curing.

Referring to FIG. 4, in order to reduce or eliminate the bow wave 44 shown in FIG. 3 caused by the region 49 (FIG. 3) of low pressure, a device 48 is installed over the radius 34 of the spar 22 and the lower flange 26 of the stiffener 21. The device 48 includes a first, bottom caul 50 covering the radius 34 of the spar 22, including the upper edge 45. The upper extremity 56 of the first caul 50 abuts the outer end 26 of the lower flange 26. The device 48 further includes a second, top caul 52 that rests on the lower flange 26 and overlies the upper extremity 56 of the first caul 50. The second caul 52 overlaps the upper extremity 56 of the first caul 50 by a preselected distance D. As will be discussed below in more detail, in one embodiment, the first and second cauls 50, 52 may be integrated into a single unit, while in other embodiments they may be separate units. A vacuum bag 83 is sealed over the assembly 20 and is used to apply compaction pressure to the parts and the caul 48.

As shown in FIG. 5, the first caul 50 includes an inside radius R substantially conforming to the radius 34. The first caul 50 has a thickness T at its upper extremity 56 which generally matches the combined thickness of the lower flange 26 and the layer of adhesive 30. The first caul 50 is tapered in its thickness from its upper extremity 56 to its lower extremity 58. The reduced thickness of the lower extremity 58 resulting from this tapering may reduce mark-off imparted to the spar 22 by the first caul 50 during the compaction process. In other embodiments, the first caul 50 may not be tapered in its thickness.

Referring to FIG. 6, the second caul 52 includes a slotted web 52 a covering the web 28 of the stiffener 21, and longitudinally extending flanges 52 b which overlie the flanges 26 on the stiffener 21.

Referring to FIG. 4 in use, the device 48 is installed either as two separate units or as a single unit on the assembly 20, such that the first caul 50 overlies the radius 34 and has its upper extremity 56 abutting the outer end 26 a of the flange 26. The slotted web 52 a of the second caul 52 is sleeved over the sides of the web 28 such that the flanges 54 rest on the flanges 26 of the stiffener 21 and the outer end 60 overlies and rests on the upper extremity 56 of the first caul 50. With the device 40 installed as described above, the vacuum bag 44 may be installed over the assembly 20, and the assembly 20 may be processed in an autoclave where pressure P is applied to the assembled parts. The first caul 50 applies and distributes the autoclave pressure P to the radius 34 including the upper extremity 56 which overlies the upper edge 45 of the radius 34. The autoclave pressure P also presses the flanges 52 b against the flanges 26 of the stiffener 21 and against the upper extremity 56 of the first caul 50.

Pressure applied to the lower flanges 26 is transferred by the second caul 52 to the first caul 50. The tendency of the upper plies 42 (FIG. 3) to produce a bow wave 44 at the edge 45 is resisted by the pressure applied to the upper extremity 56 by the forward end 60 of the second caul 52. Thus, the upper plies 32 (FIG. 3) within the radius 34 are constrained to remain substantially in-plane during the compaction process. Integrating the caul portions 50, 52 into a single part unit provide the device 48 with additional stiffness 48 which may aid in resisting generation of a bow wave 44 (FIG. 4) or similar heaving or wrinkling of the outer plies 42 at the radius edge 45.

FIGS. 7 and 8 illustrate additional details of the second caul 52. The upstanding web 52 a includes a longitudinally extending slot 62 therein, and the flanges 52 b extend laterally outward from the web 52 a. The forward end 60 extends beyond the web 52 a and is adapted to overlie the upper extremity 56 on the first caul 50, as shown in FIG. 4. The second caul 52 may be fabricated from any suitable materials that possess the requisite strength and stiffness, including but not limited to a fiber reinforced resin composite such as, without limitation, carbon fiber reinforced epoxy resin. During installation of the second caul 52, the slot 62 receives the web 28 of the stiffener 21 is received within the slot 62, and the flanges 52 b rest on the flanges 26 of the stiffener 21.

FIG. 9 illustrates another embodiment of the device 48 in which the first and second cauls 50, 52 are integrated into a single unit which may be manufactured by molding the caul 48 around the end of the stiffener 21.

Attention is now directed to FIGS. 10, 11 and 12 which illustrate another embodiment of the device 20 in which multiple devices 48 are integrated into a unitized structure. In the illustrated example, two one piece cauls 48 are arranged side by side and formed integral with a connecting portion 66 and outer extensions 68. The first cauls 50 extend substantially continuously across the entire length of the device 48. As shown in FIG. 12, the device 48 may be installed as a single unit over two adjacent stiffeners 21, covering the radius 34 on the spar 22 (not shown in FIGS. 10-12). While the embodiment shown in FIGS. 10-12 integrates multiple devices 48 for use with multiple stiffeners 21 have an I-shape cross section, the multiple integrated devices 48 may also be adapted for use with stiffeners having other cross sectional shapes, including, without limitation, C, J, Z, L and inverted U shapes.

Attention is now directed to FIG. 13 which illustrates another method of compressing a radius 34 in a manner that reduces bow waves generated during consolidation of the spar 30. In this example, the spar 30 is laid up over a mandrel 38 having a lateral extension 38 a. The lateral extension 38 a includes a curved tool surface 70 that forms an excess outwardly turned flange 72 having a large radius 74 which is generally larger than radius 34. “Excess” refers to the fact that the primary purpose of the flange 72 is to place the fibers in the radius 34 in tension, and that the flange 72 may not have other substantial functional purpose. When consolidation pressure P is applied to the spar 30, pressure acting on the large radius flange 72 is greater than that applied to the radius 34 and creates tension in the fibers in the upper plies 42 (FIG. 3) which is transferred to the fibers in the radius 34. This tension applied to the fibers in the upper plies 42 in the radius 34 may reduce or eliminate wrinkling and/or bow waves 44 in the area of the radius 34, including the upper edge 45 (FIG. 3). As used herein, “large” radius refers to a radius 74 that is large enough to produce the tension in the upper plies 42 necessary to reduce or eliminate the bow waves 44.

Attention is now directed to FIG. 14 which illustrates a method of joining composite parts in a manner that reduces bow waves in laminates during curing. At step 76, first and second parts 21, 22 are assembled. Next at step 78, a first portion 50 of a caul 48 is placed on the radius 34 of the first part 22 covering an edge 45 of the radius 34 and abutting the first part 21. At step 80, a second portion 52 of the caul 48 is installed on the second part 21, at least partially overlapping the first caul 50 at the radius edge 45. In those embodiments where the caul portions 50, 52 are integrated into a single unit, then steps 78 and 80 are combined into a single operation. At step 82, the assembled parts 21, 22 having the caul portions 50, 52 installed thereon are vacuum bagged. At 84, a vacuum is drawn and consolidation pressure is applied to the bag, using for example, autoclave processing. At step 86, caul portions 50, 52 are used to apply pressure to the radius 34 including the radius edge 45 in order to transfer atmospheric pressure loads to the radius edge 45 and reduce the formation of bow waves in the first part.

FIG. 15 illustrates the steps of a method of reducing bow waves in a laminate using the apparatus shown in FIG. 14. At step 88, a large radius 74 is formed in a laminate part 21 adjacent a smaller radius section 34 in the part 21. At step 80, compaction pressure is applied to the part 21, including applying tension on the fibers in the radius section 34 by compressing the fibers in the large radius 74.

Referring next to FIGS. 16 and 17, embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method 98 as shown in FIG. 16 and an aircraft 100 as shown in FIG. 17. During pre-production, exemplary method 92 may include specification and design 102 of the aircraft 100 and material procurement 104. During production, component and subassembly manufacturing 106 and system integration 108 of the aircraft 100 takes place. During step 106, the disclosed method and apparatus may be employed to fabricate composite parts such as fuselage sections which are then assembled at step 108. Thereafter, the aircraft 100 may go through certification and delivery 110 in order to be placed in service 112. While in service by a customer, the aircraft 100 may be scheduled for routine maintenance and service 114 (which may also include modification, reconfiguration, refurbishment, and so on).

Each of the processes of method 98 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on.

As shown in FIG. 17, the aircraft 100 produced by exemplary method 98 may include an airframe 116 with a plurality of systems 118 and an interior 120. The disclosed method and apparatus may be employed to fabricate fuselage sections which form part of the airframe 110. Examples of high-level systems 118 include one or more of a propulsion system 122, an electrical system 124, a hydraulic system 126 and an environmental system 128. Any number of other systems may be included. Although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry.

The apparatus embodied herein may be employed during any one or more of the stages of the production and service method 98. For example, components or subassemblies corresponding to production process 106 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft 100 is in service. Also, one or more apparatus embodiments may be utilized during the production stages 106 and 108, for example, by substantially expediting assembly of or reducing the cost of an aircraft 100. Similarly, one or more apparatus embodiments may be utilized while the aircraft 100 is in service, for example and without limitation, to maintenance and service 114.

Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art. 

What is claimed:
 1. A method of reducing bow wave formation in a composite laminate part during consolidation, comprising: forming a composite laminate part comprising a first component bonded to a second component, wherein forming further comprises: placing the composite laminate part in a vacuum bag; and evacuating the vacuum bag, which creates a first compaction pressure around a majority of the composite laminate part and a second compaction pressure, lower than the first compaction pressure, applied to the remainder of the composite laminate part and being located at a region at a base of a co-bonded composite structure where the vacuum bag stretches over an area of the composite laminate part rather than pressing against the composite laminate part during evacuation; and immediately after forming the composite laminate part, transmitting atmospheric pressure loads to the region at the base of the co-bonded composite structure where the vacuum bag stretches over an area of the composite laminate rather than pressing against it.
 2. The method of claim 1, wherein the region at the base of the co-bonded composite structure is located at an edge of a radius in the composite laminate part, and transmitting atmospheric pressure loads includes applying the transmitted pressure loads at the edge of the radius.
 3. The method of claim 1, wherein transmitting atmospheric pressure loads includes placing a caul on the composite laminate part at the region at the base of the co-bonded composite structure.
 4. A method of reducing a bow wave produced in a region at the base of a co-bonded composite structure having a first uncured composite part during consolidation in a vacuum bag with a second composite part, comprising: placing a caul device over the first uncured composite part and the second composite part covering the region at the base of a co-bonded composite structure; and using the caul device to apply atmospheric pressure loads to the region at the base of a co-bonded composite structure having the first uncured composite part.
 5. The method of claim 4, wherein the region at the base of a co-bonded composite structure is along an edge of a radius on the first uncured composite part, and placing the caul device includes: placing a first caul over the radius and the edge of the radius on the first uncured composite part, and placing a second caul on the second composite part overlapping the first caul.
 6. The method of claim 5, wherein using the caul device to apply atmospheric pressure loads includes using the second caul to apply pressure to the first caul in the region at the base of a co-bonded composite structure.
 7. A method of fabricating a composite structure assembly including a laminate spar joined to a stiffener having a flange, comprising: forming and precuring the stiffener to create a precured stiffener; laying up the laminate spar on a mandrel having a second radius; assembling the precured stiffener with the laminate spar, including placing a layer of adhesive between the flange of the stiffer and a web of the spar; installing a caul device on the composite structure assembly, including molding a first portion of the caul device to an end of the stiffener overlying the flange of the stiffener, and molding a second portion, having an extremity overlying the first portion, to conform to a third radius formed in the spar; vacuum bagging the composite structure assembly; placing the composite structure assembly in an autoclave; and using autoclave pressure to consolidate the composite structure assembly, including using the caul device to transmit pressure from the flange to an edge of the third radius formed in the spar.
 8. The method of claim 2, wherein transmitting atmospheric pressure loads includes placing a caul on the composite laminate part at the region at the base of the co-bonded composite structure.
 9. The method of claim 1, wherein applying the second compaction pressure further includes: placing a vacuum bag over the fiber reinforced, laminate part; placing the fiber reinforced laminate part covered by the vacuum bag in an autoclave; drawing a vacuum in the vacuum bag; and applying pressure to the vacuum bag using the autoclave. 